Girma:
Thank you for giving me the opportunity to clarify. The IPCC models are not predictive models. Thus, when climatologists such as Kevin Trenberth state that the models make no predictions, they are correct in saying so. As they make no predictions, the models cannot be statistically tested. It can be concluded that the IPCC’s inquiry into global warming was not a scientific inquiry from the lack of falsifiability of its models.
The “predictions” of a predictive model have a one-to-one relationship to independent events in a statistical population. A “prediction” is an extrapolation from an observed state of a system to an unobserved but observable state of the same system. The latter state is called the “outcome” of the associated event. The former state is called the “condition,” for it is a condition on the model’s independent variables.
A predictive model is tested by comparison of the predicted to the observed relative frequencies of all of the various possible outcomes. If there is not a match, the model is falsified by the evidence. Otherwise, it is “validated.”
The climatologists who designed the IPCC’s inquiry into global warming blundered by failing to describe this inquiry’s statistical population. In failing to describe it, they ensured that their inquiry would not be “scientific.” In its assessment reports, the IPCC covered up this blunder by claiming that the methodology of the inquiry was “scientific” because it was conducted by people calling themselves “scientists.” I describe this phenomenon in more detail in the article at http://judithcurry.com/2011/02/15/the-principles-of-reasoning-part-iii-logic-and-climatology/ .
In answer to your question, the IPCC’s statement is irrelevant, for it serves neither to falsify nor to validate the IPCC’s models. It can neither falsify nor validate them because:a) these models are not predictive models and b) the statistical population that is required for testing the models does not exist. Widespread confusion of “predictions” with “projections” serves to cover up the blunder that was made by those climatologists who designed of the IPCC’s inquiry. In blogging, my purpose is to force climatologists to own up to and fix their error.